Two things...
Tranny coolers SUCK for this application, you want a heatercore.
My personal stamp of approval goes to a 1984 Chevette core. I used mine for a year before I went to water chilling, and it worked great. One of the pipes is flared up to 5/8"or so, but if you cut it off just before the flare, you have 1/2" in and out.
The second point I wanted to make...
I'd skip the GF4 mod for now, since you are going to take enough risks with your cpu to start, while you learn. As you said, this project is more for noise control, so modding an expensive 3D card isn't really a priority is it? Just ask yourself, "can I afford to break it?"
Especially with you using a T-bird, I slaughtered a few t-birds and durons in the early days, with chipped cores, so you might want to keep some funds in reserve...just incase.
I recommend wading into this...not swan diving.
I started into water because of noise as well...two years later, I've got something most mad scientists would be proud of, and although quiet has always been the motivation, I love the extra OC'ing too.